chore(desktop): zero eslint/typecheck debt + prettier pass (#39100)

- eslint --fix across src/ and electron/ (unused imports, import/prop sort, padding)
- flatten empty catch blocks in electron CJS; drop unused applyUpdatesPosixInApp arg
- add setMutableRef helper for imperative ref writes (react-compiler clean)
- move sidebar cookie persistence into an effect; extract scrollElementToBottom helper

apps/desktop/src/app/session/hooks/use-message-stream.ts

@@ -326,10 +326,7 @@ export function useMessageStream({
       return
     }
 
-    flushHandleRef.current = window.setTimeout(
-      runFlush,
-      Math.max(0, STREAM_DELTA_FLUSH_MS - sinceLast)
-    )
+    flushHandleRef.current = window.setTimeout(runFlush, Math.max(0, STREAM_DELTA_FLUSH_MS - sinceLast))
   }, [flushQueuedDeltas])
 
   const queueDelta = useCallback(